In modern detergents, sodium percarbonate is increasingly used as a bleaching component in addition to sodium perborate because of its tendency to release active oxygen. However, the release of oxygen should not occur prematurely and thus a stabilizer which regulates the release of oxygen is added to these compounds. It is an important task to stabilize such a compound to such an extent that it can be stored both separately and in contact with the usual detergent components without significant losses of active oxygen.
The problem of stabilizing sodium perborate has been solved to a great extent. This stabilization is effected by adding a known stabilizer, such as, for example, magnesium sulfate, sodium silicate, ethylenediaminetettraacetic acid and others, during the manufacturing process. However, these stabilizing processes cannot be applied to sodium percarbonate in the same manner. This is partly due to the different molecular structure of the percarbonate and partly due to the fact that the process of crystallization from solutions or suspensions can easily be disturbed by the addition of foreign substances so that crystals are formed which are unsuitable for practical uses. The technique of stabilizing percarbonate with silicates which until now has been widely used, has not yet led to satisfactory results.
A common process for manufacturing sodium percarbonate comprises reacting a hydrogen peroxide solution with a sodium carbonate solution or suspension possibly with the simultaneous addition of sodium chloride for salting out the percarbonate and recycling the resulting mother liquor into the process after the crystallized sodium percarbonate has been separated. In this process waterglass can be added to the sodium carbonate solution or suspension as a stabilizer.
Various difficulties are connected with the addition of the waterglass solution before or during the crystallization process. If the quantity added is small, the crystallization is not adversely affected by a precipitation of insoluble silicates, but the resulting end products are not sufficently stabilized. If the quantity added is relatively high, the resulting products have a satisfactory stability but there are problems in carrying out the process. The crystallization process is disturbed; an undesirable amount of fine particles is formed, and nuclei formation and crystal growth occur largely in an uncontrolled manner. This leads to disturbances in the production process and the dehydration of the resulting percarbonate crystal suspension becomes difficult. If further quantities of waterglass are added, the above difficulties become even more pronounced and the chemical stability of the percarbonate again decreases.
Until now, therefore, it was not possible to provide the trade with a percarbonate satisfying high stability requirements in industrially needed quantities.